Impellers, specifically traditional non-constrained vane machines involving reciprocating vanes according to the prior art suffer various disadvantages. In such machines the vane or vanes ride in a slot and are pushed outwardly via centrifugal force, fluid pressure, springs or a combination of these elements such that the vanes ride in direct contact with the bore of the machine. The efficiency of this class of vane machines, when used in a pump or a compressor for example, tends to be low due to friction, which also causes accelerated wear, thereby shortening machine life. Another class of vane machines, known as constrained vane machines, have mechanisms which control the motion of the vanes and prohibit them from running in direct contact with the bore of the machine. This reduces the aforementioned friction associated with non-constrained machines and consequently decreases wear and increases efficiency. However, the design of such machines is often complicated, with many moving parts, which limits the speed at which such impellers may run safely. Machine cost and reliability may also be adversely affected. There is a clear demand for improved impeller designs which do not suffer the manifest disadvantages of prior art devices.